Heat-treatment effect on the nanosized graphite π-electron system during diamond to graphite conversion
Heat-treatment effect on the nanosized graphite π-electron system during diamond to graphite conversion
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金刚石转化为石墨过程中热处理对纳米石墨π电子体系的影响
DOI：
10.1103/physrevb.62.11209
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发表时间：
2000
影响因子：
3.7
通讯作者：
M. Endo
中科院分区：
文献类型：
--
作者：
B. Prasad;H. Sato;T. Enoki;Y. Hishiyama;Y. Kaburagi;A. M. Rao;P. Eklund;K. Oshida;M. Endo
石墨纳米颗粒是通过在 900\char21{}1600\ifmmode^\circ\else\text Degree\fi{}C 范围内对金刚石纳米颗粒进行热处理而制备的。 X 射线衍射、透射电子显微镜 (TEM) 和拉曼散射研究表明，金刚石-石墨转变的起始温度约为 1200 \ifmmode^\circ\else\text Degree\fi{}C，金刚石完全转变为石墨的温度为 1600 \ifmmode^\circ\else\text Degree\fi{}C。根据结构特征，样本被分为 ${\mathrm{sp}}^{3}$ 主导（按原样和 900 \ifmmode^\circ\else\text Degree\fi{}C）、${\mathrm{sp}}^{2}{:sp}^{3}$ 混合相（1200 和 1400 \ifmmode^\circ\else\text Degree\fi{}C），以及${\mathrm{sp}}^{2}$主导的系统（1600 \ifmmode^\circ\else\text Degree\fi{}C）。 ${\mathrm{sp}}^{2}{:sp}^{3}$ 混合相系统的较大 c 轴重复距离和高分辨率 TEM 图像表明石墨烯片中存在金刚石 (111) 平面的残余屈曲特征。磁化率和 ESR 研究表明，从 1200 \ifmmode^\circ\else\text Degree\fi{}C 和更高温度的热处理样品中发展出了巡回-\ensuremath{\pi}-电子系统。完全石墨化的样品揭示了边缘继承的非键合\ensuremath{\pi}电子态在电子结构中的重要作用。拉曼 G 峰位置和轨道抗磁性与块体石墨值存在相当大的偏差，这是根据从石墨 \ensuremath{\pi} 带到局部边缘态的电荷转移以及由此产生的费米能级移动来解释的。在 1400 和 1600 \ifmmode^\circ\else\text Degree\fi{}C 下热处理更多石墨化样品的情况下，增强的自旋晶格弛豫率预计是由于局域边缘态电子的参与而产生的。然而，在石墨化程度较低的 1200 \ifmmode^\circ\else\text Degree\fi{}C 热处理样品中，石墨烯平面的波纹性质可能会阻碍这种快速弛豫过程。
Graphite nanoparticles were prepared by the heat treatment of diamond nanoparticles in the range 900\char21{}1600 \ifmmode^\circ\else\textdegree\fi{}C. X-ray diffraction, transmission electron microscopy (TEM) and Raman scattering studies indicate that the onset temperature of the diamond-graphite transition is around 1200 \ifmmode^\circ\else\textdegree\fi{}C and the complete conversion of diamond to graphite occurs at 1600 \ifmmode^\circ\else\textdegree\fi{}C. Based on the structural characteristics the samples are categorized into ${\mathrm{sp}}^{3}$-dominated (as-prepared and 900 \ifmmode^\circ\else\textdegree\fi{}C), ${\mathrm{sp}}^{2}{:sp}^{3}$ mixed-phase (1200 and 1400 \ifmmode^\circ\else\textdegree\fi{}C), and ${\mathrm{sp}}^{2}$-dominated systems (1600 \ifmmode^\circ\else\textdegree\fi{}C). The larger c-axis repeat distances and the high-resolution TEM images for the ${\mathrm{sp}}^{2}{:sp}^{3}$ mixed-phase systems denote the presence of the remnant buckling feature of the diamond (111) planes in the graphene sheets. Magnetic susceptibility and ESR studies suggest the development of itinerant-\ensuremath{\pi}-electron system from the 1200 \ifmmode^\circ\else\textdegree\fi{}C and higher-temperature heat-treated samples. The completely graphitized sample reveals the important role of edge-inherited nonbonding \ensuremath{\pi}-electron states in the electronic structure. The Raman G-peak position and the orbital diamagnetism show considerable deviation from the bulk-graphite values, which is explained on the basis of charge transfer from the graphite \ensuremath{\pi} band to the localized edge states and the resulting shifting of the Fermi level. The enhanced spin-lattice relaxation rates in the case of more graphitized samples heat-treated at 1400 and 1600 \ifmmode^\circ\else\textdegree\fi{}C are expected to arise from the involvement of the localized edge-state electrons. In the less-graphitized 1200 \ifmmode^\circ\else\textdegree\fi{}C heat-treated sample, however, the corrugated nature of the graphene planes is likely to hinder such fast-relaxation processes.